CognitiveClouds React Js Frontend Developer Interview Questions and Answers

Q1. What is prop drilling
Ans. 
Prop drilling is the process of passing props down multiple levels of nested components in React.
• Prop drilling occurs when a prop needs to be passed through multiple levels of components that do not need the prop themselves.

• It can lead to unnecessary passing of props through intermediate components, making the code harder to maintain.

• To avoid prop drilling, you can use Context API, Redux, or React's useContext and useR...read more
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Q2. What is hoisting
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Hoisting is a JavaScript mechanism where variable and function declarations are moved to the top of their containing scope during the compilation phase.
• Variable declarations are hoisted to the top of their scope, but not their assignments.

• Function declarations are fully hoisted, meaning they can be called before they are declared.

• Hoisting can lead to unexpected behavior if not understood properly.
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Q1. Explain useContext hook
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useContext hook allows components to access data from a context without passing props down manually
• useContext hook is used to consume a context created by React.createContext

• It takes the context object as an argument and returns the current context value for that context

• It allows components to subscribe to context changes and re-render when the context value changes
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Q1. What is the difference between debounce and throttling
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Debounce delays the execution of a function until after a specified time period, while throttling limits the rate at which a function can be executed.
• Debounce waits for a specified time period of inactivity before executing the function, while throttling limits the rate at which the function can be called.

• Debounce is useful for scenarios like search bars where you want to wait for the user to finish typing before makin...read more
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Q2. What was used before Rest APIs
Ans. 
SOAP (Simple Object Access Protocol) was used before Rest APIs for web services communication.
• SOAP was a protocol for exchanging structured information in the implementation of web services.

• SOAP used XML for message format and relied heavily on HTTP for communication.

• SOAP was more rigid and complex compared to Rest APIs, which are more lightweight and flexible.

• Examples of SOAP-based web services include Microsoft's .NE
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Q1. Frontend developer
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Html, CSS, bootstrap, JavaScript, react.js

Q1. All javascript core concepts and react hooks
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Find the max values, promises, async await

Q1. Object , array , ES6, React basics
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Q1. Advance Javascript questions
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Q2. React application with custom hooks
Ans. 
Custom hooks in React allow for reusable logic across components.
• Custom hooks are functions that use React hooks internally and can be reused across multiple components.

• They can encapsulate complex logic and state management, making components more modular and easier to maintain.

• Example: A custom hook for fetching data from an API and handling loading and error states can be used in multiple components.

• Example: A custo...read more
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Q1. Roles & Responsibilites
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Q1. Types of Promises
Ans. 
Promises in JavaScript are objects representing the eventual completion or failure of an asynchronous operation.
• Promises can be in one of three states: pending, fulfilled, or rejected.

• Promises can be chained using .then() to handle success and .catch() to handle errors.

• Promises can be created using the Promise constructor or by using async/await syntax.
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Q2. Difference between useState and useEffect
Ans. 
useState is used to manage state in functional components, while useEffect is used to perform side effects in functional components.
• useState is used to declare state variables in functional components.

• useEffect is used to perform side effects in functional components, such as data fetching, subscriptions, or manually changing the DOM.

• useState does not trigger re-renders, while useEffect can be used to trigger re-render...read more
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Q3. What is Callback hell
Ans. 
Callback hell is a situation where multiple nested callbacks make the code difficult to read and maintain.
• Occurs when multiple asynchronous operations are nested within each other

• Leads to deeply nested code structure which is hard to understand

• Can be avoided by using Promises, async/await, or modularizing code
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Q4. Difference between traditional function and arrow function
Ans. 
Traditional functions are defined using the function keyword, while arrow functions are defined using a concise syntax with =>.
• Traditional functions are hoisted, while arrow functions are not.

• Arrow functions do not have their own 'this' keyword, they inherit it from the parent scope.

• Arrow functions are more concise and easier to read compared to traditional functions.

• Traditional functions are better for methods in obje...read more
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Q5. Usecase to create counter in react
Ans. 
Creating a counter in React to increment and decrement a value.
• Create a state variable to store the count value

• Use setState to update the count value

• Render the count value in the component

• Add buttons to increment and decrement the count value
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Q6. Program to find frequency of letters in a string
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Program to find frequency of letters in a string
• Create an object to store the frequency of each letter

• Loop through the string and increment the count of each letter in the object

• Convert the object into an array of strings with letter and frequency pairs
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Q7. Program to find if substring is present in a given string without using predefined functions
Ans. 
Iterate through the given string to check if the substring is present.
• Iterate through the given string and check if each character matches the first character of the substring.

• If a match is found, check the subsequent characters to see if they form the substring.

• Return true if the entire substring is found within the given string, otherwise return false.
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